The invention relates to a method and device for monitoring and/or determining motor oil quality by determining the viscosity of the motor oil being used by internal combustion engines.
Many known devices such as machine tools and motor vehicles must be serviced in certain intervals in order to ensure their reliability and extend their service life. The motor oil used by the engine of a motor vehicle is subject to degradation and must be changed after reaching a certain degree of degradation, to avoid engine damage due to insufficient lubrication and cooling. The service life of a motor oil depends, however, on many operating parameters, such as environmental conditions and the driver""s driving style. Since these are not predictable, certain safety margins are used and the manufacturer specifies fixed service intervals and oil change intervals for the sake of simplicity, expressed, for example, as fixed mileage figures, and which must be observed for the manufacturer""s warranty to remain valid. This results in the vehicle owner often having the vehicle serviced or the oil changed without any valid technical reason, which represents a considerable additional cost factor. Therefore, considerable efforts have been made for some time to match the oil change intervals to the actual degradation of the motor oil.
Known methods for directly determining the degree of motor oil degradation or contamination include, for example, measuring the electrical resistance of the oil the pressure differential between upstream and downstream sides of the oil filter, transparency, or chemical composition of the motor oil. The disadvantage of these direct methods is the additional cost of measuring, for example, the need for additional and special sensors, etc. Therefore, in addition to direct measuring methods, there are methods in which the degree of degradation of the motor oil is determined from operating parameters of the engine or the vehicle that are known otherwise.
European Patent 174 601 discloses a warning system that measures and displays the degradation or aging of the oil in an internal combustion engine and emits a warning signal. The condition of the oil is evaluated and the result of the evaluation is output based on engine parameters such as rotation speed, instantaneous engine load, and oil temperature.
German Patent 41 31 969 presents a lubricating oil monitoring system, in which the oil parameters such as pressure, temperature, and viscosity are measured using a special sensor chip and the actual condition of the motor oil is derived from these parameters. The viscosity of the motor oil is determined using capacitive measurement of the dielectric constant of the oil at two different frequencies. As an alternative, the viscosity of the motor oil can also be determined by measuring sound wave dampening in the motor oil.
German Patent 32 28 195 discloses a method and a device for monitoring the time for a lubricating oil change in a vehicle engine. One essential step of this method is the determination of the contaminant level in the motor oil, which can be derived from the operating conditions of the engine, the level of contaminants being in direct relationship to the viscosity of the motor oil.
The disadvantage of the known methods is that either additional sensors are needed or the conclusion regarding the degree of degradation of the motor oil from known operating parameters does not have the required accuracy and therefore, for safety reasons, the motor oil is changed too early, resulting in extra cost to the owner of the vehicle.
An object of the present invention is therefore to develop a method and device that provide for the motor oil quality of a motor vehicle engine to be monitored and/or determined in a simple and accurate manner.
This object is achieved by determining and evaluating changes in oil viscosity as a function of temperature and engine frictional torque. The method according to the present invention allows changes in motor oil viscosity, which in turn are used for monitoring the motor oil quality, to be determined in a reliable manner as a function of the engines temperature and frictional torque. If the motor oil quality is known, an oil change is not required until the motor oil has actually degraded.
In a preferred embodiment of the method the engine frictional torque is derived from the starting torque. This allows the engine frictional torque to be determined in a simple manner.
In another advantageous embodiment of the present invention, the starting torque is determined from the electric power consumed by the starter during start, with the starter characteristics being known. This method is particularly simple, since current consumption essentially corresponds to the battery load and is therefore easy to determine. Current consumption as a function of motor oil quality is therefore simple to use for determining or evaluating quality.
Advantageously, changes in viscosity are not taken into account unless the value (actual value) is outside a range of xe2x88x9215% to +50% of a predefined viscosity value at the same temperature. This prevents slight variations in viscosity due to different marginal parameters resulting in an xe2x80x9coil change neededxe2x80x9d display. It is ensured that only significant changes are taken into account in monitoring and subsequent action is not taken before the right time.
The object of the present invention is furthermore achieved by determining motor oil quality, particularly the viscosity, in an internal combustion engine as a function of engine temperature and frictional torque. By determining the viscosity of the motor oil from the engine frictional torque, with the latter being determined from data present in an engine controller, the proper time for oil change is determined in a simple manner.
In the case of a gasoline engine, the following engine data may be advantageously used for determining the engine frictional torque; i) injection time and/or throttle valve position to determine the engine torque produced; ii) a clutch switch signal, showing whether torque is being transmitted to the drive train; iii) the load signal of the generator to determine the generator drive torque; iv) and signals concerning the operating state of any other auxiliary devices directly driven by the engine. Thus, reliable determination of the motor oil quality is provided.
In a diesel engine, the following engine data may be for determining the frictional torque; i) a clutch switch signal, which shows whether torque is being transmitted to the drive train; ii) the generator load signal as a measure of the electric power generated by the generator; iii) engine rpm; the injected amount of fuel; the engine temperature; and iv) the ambient temperature. This allows the engine oil quality to be reliably determined.
The object of the present invention can also be realized using a method of determining the motor oil viscosity in an internal combustion engine. By measuring the time from start at the engine to the moment when the starter disengagement speed is reached, so that if the constant fuel amount injected during this time is known, the engine frictional torque can be derived from the measured time, and the motor oil quality can be reliably and accurately estimated therefrom.
The object of the present invention can also be realized using a device for carrying out the method. In order to determine viscosity, this device has a control unit for processing and transforming data and at least one memory, with the characteristic curves, needed for determining the viscosity being stored in the memory or in each memory. Such a device allows the motor oil quality to be determined in a simple manner, since no additional measuring means are needed.